A rash? Vagisil is not meant to treat a rash. You could have a yeast infection, that causes itching, but not usually a rash that starts in the anus and spreads, that sounds more like an std or something else. Yeast infections usually present with itching and discharge that is like cottage cheese, as well as irritation in the vagina and pain during sex.
Why are you using a feminine wash? It's completely unnecessary and may cause more harm than good.
You need to see a doctor if it's spreading. Have you had unprotected sex? IF so, sounds like an std. Get yourself to the doc.